In recent years, along with the development of communication networks, high-speed computers, and large-size storage media, higher image quality is demanded upon handling color image information. Above all, a demand for accurately reading color image information at high speed and with high image quality using a scanner or the like is increasing.
Also, upon reading an image on a photo film, a demand for accurately reading photo film image information of a sleeve form having a plurality of frames at high speed and with high image quality is increasing. In order to read a film image with higher image quality, an image reading apparatus having dust/scratch removal processing unit on a film has been proposed, and Japanese Patent Laid-Open No. 2001-298593 is known as such example. According to this proposal, a light source, which has an infrared LED used to detect dust/scratch information, and a light source used to read image information, forms a surface light source, and can read an image free from the influences of dust and scratches. However, since the surface light source as an indirect illumination system has poor illumination efficiency, a method of synchronously moving an illumination system and optical system is known so as to read an image at higher speed and with higher image quality.
As the method of controlling the illumination system and optical system, Japanese Patent Laid-Open No. 10-004481 or the like is known. This proposal provides means that reduces the influences of, e.g., synchronous errors caused by positional deviation between the illumination system and optical system as much as possible. Also, as an arrangement which has a plurality of light sources, and reduces positional deviation of pixel information corresponding to the plurality of light sources by controlling the phases of ON/OFF controllers of the light sources upon reading image information while changing the light sources to be turned on by line, that is disclosed in Japanese Patent Laid-Open No. 2001-045234 is known.
An example which is designed to improve dust/scratch component removal performance from an image signal obtained by reading a transparent document will be briefly described below using FIGS. 15, 16, 17A, and 17B.
FIG. 15 is a schematic sectional view showing an example of an image reading apparatus which can read both a reflective document such as a paper document or the like, and a transparent document such as a photo film or the like, and FIG. 16 is a partially cutaway front view showing an example of a transparent document illumination device used in the image reading apparatus having a dust/scratch removal function.
An image reading apparatus 100 includes a transparent document illumination device 200 required to read a transparent document such as a photo film or the like, and the device 200 is electrically connected to an image reading apparatus control board 3 via a transparent document light source ON/OFF inverter 7 and I/F cable 15 so as to be controlled by the control board 3. The transparent document illumination device 200 has a transparent document illumination unit 18 used to read a transparent document. An optical unit 14 has a first reflection mirror 9, second reflection mirror 10, third reflection mirror 11, and lens 12, which are required to optically form a transparent document image on a CCD image sensor 13, and also a reflective document illumination light source 8 used to illuminate a reflective document such as a paper document or the like with light. The optical unit 14 reads an image while scanning in the direction of an arrow in FIG. 15 (sub-scan direction) by the image input apparatus control board 3 and a motor 16. Note that an image falling within a range specified by the optical unit 14 indicated by the dotted line, and the position of the transparent document illumination unit 18 can be read.
The CCD image sensor 13 and image input apparatus control board 3 are electrically connected via a signal cable 17. By synchronously scanning the transparent document illumination unit 18 and optical unit 14 by the motor 16, an electrical signal photoelectrically converted by the CCD image sensor 13 can be acquired as image data. A transparent plate 19 is interposed between the transparent document illumination unit 18 and a film guide 5 on a platen glass 6, and is arranged in the transparent document illumination device 200. The transparent plate 19 uses transparent glass or a diffusion material. In the transparent document illumination unit 18, a light source 4 used to read a transparent document, and an infrared LED array 27 used to acquire dust/scratch information are nearly parallelly juxtaposed, as shown in FIG. 16.
FIG. 17B shows the optical positional relationship upon synchronously scanning the transparent document illumination unit 18 and optical unit 14, and FIG. 17A is a graph showing the amounts of light of the light source 4 and infrared LED array 27. In FIG. 17A, the ordinate plots the amount of light, and the abscissa plots the position in the sub-scan direction in FIG. 17B. In order to read a film placed in the film guide 5, which is set at a predetermined position in advance, a diffusion sheet 30 is provided to make a light amount distribution L1a formed by light source 4 and a light amount distribution L2a formed by the infrared LED array 27 more homogeneous within a predetermined range (the read position of the optical unit 14) in the sub-scan direction.
Upon reading a transparent document image, the light source 4 and infrared LED array 27 are line-sequentially switched and scanned, while maintaining the positional relationship shown in FIG. 17B all the time, thus reading a high-quality image by utilizing the dust/scratch removal function in one scan.
However, it is often difficult to accurately detect position information of dust, scratches, and the like on a film.
For example, FIG. 18 simply shows a method of reducing image positional deviation.
In FIG. 18, Motor HSYNC indicates a period signal for 1 Line to be scanned by the motor 16. In 1 Line, the accumulation time (CCD Shift gate pulse period) of the CCD image sensor 13 is divided into two periods, as shown in, e.g., FIG. 18, and a signal component as image information obtained by an ON/OFF control pulse of the light source 4, and a signal component as image information obtained by a relative ON time based on an ON/OFF control pulse of the infrared LED array 27 are line-sequentially obtained as CCD output signals in these periods. However, positional deviation of image information cannot be perfectly removed by only control based on the relative ON time with respect to the light amount distributions of the respective light sources in FIG. 17A. Also, the ON times of the respective light sources may become considerably shorter than the CCD accumulation time, resulting in poor S/N.
In the method using the conventional means proposed by Japanese Patent Laid-Open No. 2001-045234, the infrared LED array 27 is required to emit a large amount of light to obtain a homogeneous light amount distribution within the range on a document corresponding to RGB, 3-line range. Hence, the cost increases due to an increase in the number of chips of the LED array.